1. Field of Invention
In the art of injection plastic molding utilizing mold members defining a mold cavity moldable thermoplastic resin compositions or materials have heretofore been introduced into such molds for defining in the molded article a smooth non-cellular skin and an internal foam body. Various problems have arisen in providing a foam plastic structural part because of the need of finishing the exterior surface thereof to render the same smooth and non-porous. In the use of blowing agents heretofore and in the introduction of cellular plastic material into a mold, the resulting part does not have in many cases a smooth, dense, solid outer surface due to the passage of gaseous materials to the mold surfaces during the molding operation resulting in pitting and irregularities formed in the surfaces. Costly hand finishing of the part was often required.
2. Description of the Prior Art
Various unsuccessful attempts have been made heretofore to mold foam plastic structural parts having smooth skins or surfaces and to commercialize same in the industry. Typical of such efforts are the following United States patents along the prior art United States and foreign patents cited therein:
______________________________________ PATENT DATE INVENTOR ______________________________________ 4,136,220 January 23, 1979 Olagoke Olabisi 4,140,672 February 20, 1979 Hiroshi Kataoka 4,201,742 May 6, 1980 James W. Hendry ______________________________________